Video quality estimation device, video quality estimation method, and video quality estimation program

ABSTRACT

A video quality estimation apparatus used for an encoded video, to estimate a video quality value being a value quantifying a video quality being quality of the video felt by a user when viewing and listening to the video. The apparatus includes a maximum value calculator to calculate a maximum value of the video quality value from a resolution of the video and a frame rate of the video, and a video quality calculator to calculate an estimated video quality value corresponding to an encoding bit rate having been input, based on a predetermined relationship between the encoding bit rate of the video and the video quality value. The predetermined relationship is a relationship in which the video quality value increases while the encoding bit rate increases, and the video quality value converges on the maximum value calculated by the maximum value calculator.

TECHNICAL FIELD

This invention relates to an apparatus, a method, and a program used ina service that provides encoded video to be viewed and listened to, forestimating quality of the video felt by a user when viewing andlistening to the video (referred to as the “video quality”, below).

BACKGROUND ART

In recent years, video distribution services through networks havebecome widespread. In order to raise the revenue, it is important forvideo distribution service providers to provide the services with thevideo quality that satisfies users. Therefore, it is important to designand manage the services based on the video quality, and this makes ademand for a technology that quantifies the video quality.

Generally, an encoding process is applied to a video to compress theamount of data. If the encoding bit rate is lowered, deformation,fading, and the like are generated in blocks that degrade the videoquality. Also, the video quality is also dependent on the resolution andthe frame rate of the video.

In order to design and manage the video distribution service, it isnecessary to take the above properties of the video quality intoaccount, and to precisely estimate the video quality in terms of theencoding bit rate, the resolution, and the frame rate.

PRIOR ART DOCUMENTS Non-Patent Documents

-   Non-patent document 1: Yuichiro Urata, Kazuhisa Yamagishi, “Validity    verification of ITU-T Recommendation P.1201.1 Model Extended for    Video Resolution”, EIC technical report, CQ2012-94, pp.59-63, March    2013

SUMMARY OF INVENTION Problem to be Solved by the Invention

This invention has been made paying attention to the situation describedabove, and the object is to provide a technology that makes it possibleto precisely estimate the video quality based on the encoding bit rate,the resolution, and the frame rate.

Means for Solving the Problem

According to an embodiment of the present invention, a video qualityestimation apparatus is provided that is used for an encoded video to beviewed and listened to, to estimate a video quality value being a valuequantifying a video quality being quality of the video felt by a userwhen viewing and listening to the video. The video quality estimationapparatus includes a maximum value calculator configured to calculate amaximum value of the video quality value from a resolution of the videoand a frame rate of the video; and a video quality calculator configuredto calculate an estimated video quality value corresponding to anencoding bit rate having been input, based on a predeterminedrelationship between the encoding bit rate of the video and the videoquality value. Here, the predetermined relationship is a relationship inwhich the video quality value increases while the encoding bit rateincreases, and the video quality value converges on the maximum valuecalculated by the maximum value calculator.

Also, according to another embodiment of the present invention, a videoquality estimation apparatus is provided that is used for an encodedvideo to be viewed and listened to, to estimate a video quality valuebeing a value quantifying a video quality being quality of the videofelt by a user when viewing and listening to the video. The videoquality estimation apparatus includes a maximum value calculatorconfigured to calculate a maximum value of the video quality value,based on a resolution being a number of pixels in one frame of the videoand a frame rate being a number of frames per unit time of the video; aninflection point calculator configured to calculate an inflection pointbeing a point at which a curving direction changes on a curve drawn by asigmoid function having a property of an S-curve that converges on acertain value when an input value increases or decreases, based on theresolution and the frame rate; and a video quality calculator configuredto calculate an estimated video quality value by inputting an encodingbit rate being an average amount of data per unit time of the video, themaximum value of the video quality value calculated by the maximum valuecalculator, and the inflection point calculated by the inflection pointcalculator, into the sigmoid function.

Also, according to another embodiment of the present invention, a methodfor estimating video quality is provided that is executed by a videoquality estimation apparatus used for an encoded video to be viewed andlistened to, to estimate a video quality value being a value quantifyinga video quality being quality of the video felt by a user when viewingand listening to the video. The method includes a maximum valuecalculating step for calculating a maximum value of the video qualityvalue from a resolution of the video and a frame rate of the video; anda video quality calculating step for calculating an estimated videoquality value corresponding to an encoding bit rate having been input,based on a predetermined relationship between the encoding bit rate ofthe video and the video quality value. Here, the predeterminedrelationship is a relationship in which the video quality valueincreases while the encoding bit rate increases, and the video qualityvalue converges on the maximum value calculated by the maximum valuecalculating step.

Also, according to another embodiment of the present invention, a methodfor estimating video quality is provided that is executed by a videoquality estimation apparatus used for an encoded video to be viewed andlistened to, to estimate a video quality value being a value quantifyinga video quality being quality of the video felt by a user when viewingand listening to the video. The method includes calculating a maximumvalue of the video quality value, based on a resolution being a numberof pixels in one frame of the video and a frame rate being a number offrames per unit time of the video; calculating an inflection point beinga point at which a curving direction changes on a curve drawn by asigmoid function having a property of an S-curve that converges on acertain value when an input value increases or decreases, based on theresolution and the frame rate; and calculating an estimated videoquality value by inputting an encoding bit rate being an average amountof data per unit time of the video, the maximum value, and theinflection point, into the sigmoid function.

Advantage of the Invention

According to an embodiment of the present invention, a technology isprovided that makes it possible to precisely estimate the video qualitybased on the encoding bit rate, the resolution, and the frame rate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a relationship between the encoding bit rate and thevideo quality value showing an example of a result of a subjectiveevaluation experiment (where the resolution is changed);

FIG. 2 illustrates a relationship between the encoding bit rate and thevideo quality value showing an example of a result of a subjectiveevaluation experiment (where the frame rate is changed);

FIG. 3 is a functional block diagram illustrating an example of aconfiguration of a video quality estimation apparatus to which a methodfor estimating video quality according to an embodiment is applied;

FIG. 4 is a diagram illustrating a relationship between the encoding bitrate and the video quality value, based on a formula for estimatingvideo quality according to an embodiment;

FIG. 5 is a diagram illustrating a relationship between the encoding bitrate and the video quality value, based on a formula for estimatingvideo quality according to an embodiment; and

FIG. 6 is a flowchart illustrating an example of operations of a videoquality estimation apparatus to which a method for estimating videoquality according to an embodiment is applied.

EMBODIMENTS OF THE INVENTION

In the following, embodiments of the present invention will be describedwith reference to the drawings. Note that the embodiments describedbelow are just examples, and embodiments to which the present inventionis applied are not limited to the following embodiments.

(Properties of Video Quality)

An example of properties of the video quality assumed in the embodimentwill be described before describing a method for estimating videoquality according to the embodiment.

FIG. 1 and FIG. 2 illustrate results of experiments in which multipleevaluators watch and evaluate a video (referred to as “subjectiveevaluation experiments”, below). In FIG. 1 and FIG. 2, the vertical axisrepresents the average of grades given by the evaluators who evaluatethe video that they have viewed and listened to (referred to as the“video quality value”, below), and the horizontal axis represents theencoding bit rate.

Different plotted points in FIG. 1 and FIG. 2 represent differentresolutions of the video in FIG. 1 and different frame rates in FIG. 2.In other words, FIG. 1 illustrates curves obtained in a state where theframe rate is fixed to 15 while the resolution is changed, namely, thecurves a (resolution 480×270), b (resolution 640×360), c (resolution960×540), and d (resolution 1280×720). Also, FIG. 2 illustrates curvesobtained in a state where the resolution is fixed to 640×360 while theframe rate is changed, namely, the curves e (frame rate 10), f (framerate 15), and g (frame rate 30).

In these subjective evaluation experiments in which either of theresolution or the frame rate is fixed, results are obtained as follows:

-   -   The encoding bit rate and the video quality value have a        relationship represented by an S-curve (Property 1);    -   When the encoding bit rate becomes small, the video quality        value converges on a minimum quality value (the video quality        value 1 in FIG. 1 and FIG. 2) (Property 2);    -   When the encoding bit rate becomes great, the video quality        value converges on a certain video quality value, which becomes        greater while the encoding bit rate becomes greater or the frame        rate becomes greater (Property 3); and    -   In addition, a result is obtained about the inflection points of        the S-curves plotted in FIG. 1 and FIG. 2 in which the        inflection point is positioned at a higher encoding bit rate in        FIG. 1 if the resolution is greater, and in FIG. 2 if the frame        rate is greater (Property 4). As an example of properties of the        video quality, Properties 1 to 4 are observed.

(Apparatus Configuration)

FIG. 3 is a functional block diagram illustrating an example of aconfiguration of a video quality estimation apparatus 10 to which amethod for estimating video quality according to the embodiment isapplied.

In the embodiment, based on the video quality value being the average ofgrades obtained by the subjective evaluation experiments, therelationship among encoding bit rate BR, resolution RS, frame rate FR,and the video quality value is modeled, and by using a derived modelformula, an estimated video quality value VQ is calculated from theencoding bit rate BR, the resolution RS, and the frame rate FR.

In order to implement this, the video quality estimation apparatus 10includes a maximum value calculator 12, an inflection point calculator14, and a video quality calculator 16. Such a video quality estimationapparatus 10 may be implemented by a computer that reads a programrecorded on, for example, a recording medium such as a magnetic disc, ora program downloaded through a communication network such as theInternet, and the operation is controlled by the program. In otherwords, the maximum value calculator 12, the inflection point calculator14, and the video quality calculator 16 are implemented by a processorof the computer that runs the program.

Alternatively, the maximum value calculator 12, the inflection pointcalculator 14, and the video quality calculator 16 may be implemented byhardware circuits, respectively.

The maximum value calculator 12 receives as input the resolution RSbeing the number of pixels in one frame of the video, and the frame rateFR being the number of frames per unit time of the video, and calculatesa maximum value MAX of the video quality value that is determined foreach resolution RS and each frame rate FR. The maximum value MAX of thevideo quality value is calculated by the following formula (Formula 1).Formula 1 is represented by a two-variable increasing function thatincreases while the resolution RS and the frame rate FR increase. Asdescribed above, when the encoding bit rate becomes great, the videoquality value converges on a certain convergence value. A maximum valueMAX here corresponds to the convergence value obtained with a resolutionRS and a frame rate FR that are given.

$\begin{matrix}{{{MAX} = {\frac{A_{1} \cdot {RS}}{c_{1} + {RS}} + {VQ}_{m\; i\; n}}}{A_{1} = {\left( {{VQ}_{{ma}\; x} - {VQ}_{m\; i\; n}} \right) \cdot \left( {1 - {\exp\left( {{- c_{2}} \cdot {FR}} \right)}} \right)}}} & {{Formula}\mspace{14mu} 1}\end{matrix}$

where c₁ and c₂ are the coefficients, VQ_(max) represents the maximumvalue that can be taken as the estimated video quality value VQ, andVQ_(min) represents the minimum value that can be taken as the estimatedvideo quality value VQ. For example, according to the ACR method, whichis a subjective evaluation method defined in ITU-T recommendation P.910,VQ_(max) is set to 5 and VQ_(min) is set to 1.

Note that the maximum value calculator 12 may include processing logiccorresponding to Formula 1 to calculate the maximum value MAX, or mayread data of the function represented by Formula 1 from a storage unitincluded in the video quality estimation apparatus 10 to execute thecalculation of Formula 1. Alternatively, according to the relationshiprepresented by Formula 1, a table may be stored in the storage unit inwhich values of the resolution RS, the frame rate FR, and the maximumvalue MAX are associated with each other, from which a maximum value MAXis read out that corresponds to the input values, to execute thecalculation.

Note that Formula 1 is just an example of a formula that calculates themaximum value MAX of the video quality value. Another formula may beused that appropriately represents the maximum value MAX of the videoquality value obtained by the experiments or the like for eachresolution RS and each frame rate FR.

The inflection point calculator 14 calculates an inflection point IP byusing the resolution RS and the frame rate FR. The inflection point IPis a point at which the curving direction changes on a curve drawn by asigmoid function used in the video quality calculator 16. The sigmoidfunction has the property of S-curve that the value converges on acertain value when the input value increases or decreases. Theinflection point IP is calculated by the following formula (Formula 2).Formula 2 is represented by a two-variable increasing function thatincreases while the resolution RS and the frame rate FR increase.

$\begin{matrix}{{{IP} = \frac{{c_{3} \cdot {RS}} + A_{2}}{1 - e^{{- c_{6}} \cdot {RS}}}}{A_{2} = {c_{4} \cdot {\log_{e}\left( {{c_{5} \cdot {FR}} + 1} \right)}}}} & {{Formula}\mspace{14mu} 2}\end{matrix}$

where c₃, c₄, c₅, and c₆ are the coefficients. Note that the unit of theinflection point IP is the same as the unit of the encoding bit rate.

Note that the inflection point calculator 14 may include processinglogic corresponding to Formula 2 to calculate the inflection point IP,or may read data of the function represented by Formula 2 from a storageunit included in the video quality estimation apparatus 10 to executethe calculation of Formula 1. Alternatively, according to therelationship represented by Formula 2, a table may be stored in thestorage unit in which values of the resolution RS, the frame rate FR,and the inflection point IP are associated with each other, from whichan inflection point IP is read out that corresponds to the input values,to execute the calculation.

Note that Formula 2 is just an example of a formula that calculates theinflection point IP. Another formula may be used that appropriatelyrepresents the inflection point IP obtained by the experiments or thelike for each resolution RS and each frame rate FR.

The video quality calculator 16 receives the encoding bit rate BR as theinput value, and calculates the estimated video quality value VQrepresented by the sigmoid function to which a maximum value MAX of thevideo quality value and an inflection point IP are applied. An exampleof such a sigmoid function is illustrated by the following Formula 3.

$\begin{matrix}{{VQ} = {{MAX} + \frac{{VQ}_{m\; i\; n} - {MAX}}{1 + \left( \frac{BR}{IP} \right)^{c_{7}}}}} & {{Formula}\mspace{14mu} 3}\end{matrix}$

where c₇ appearing as the exponent of (BR/IP) is the coefficient. Assuch, the estimated video quality value VQ is represented by the sigmoidfunction taking the encoding bit rate BR as input. The coefficient c₇ isdetermined so that the higher convergence value of the encoding bit rateBR becomes the maximum value MAX of the video quality value, and thelower convergence value of the encoding bit rate BR becomes the minimumvalue MIN of the video quality value. Also, the inflection point IPcorresponds to the X-axis coordinate of the inflection point of thesigmoid function.

Note that c₁, c₂, c₃, c₄, c₅, c₆, and c₇ may be determined by the methodof least squares or the like so as to be optimized in a sense that thedifference becomes minimum between the video quality value and theestimated video quality value VQ obtained by the subjective evaluationexperiments.

Note that the video quality calculator 16 may include processing logiccorresponding to Formula 3 to calculate the estimated video qualityvalue VQ, or may read data of the function represented by Formula 3 froma storage unit included in the video quality estimation apparatus 10 toexecute the calculation of Formula 3. Alternatively, according to therelationship represented by Formula 3, a table may be stored in thestorage unit in which values of the maximum value MAX, the inflectionpoint IP, the encoding bit rate BR, and the estimated video qualityvalue VQ are associated with each other, from which an estimated videoquality value VQ is read out that corresponds to the input values (themaximum value MAX, the inflection point IP, and the encoding bit rateBR), to execute the calculation.

Also, a formula that calculates the estimated video quality value VQfrom the maximum value MAX of the video quality value, the inflectionpoint IP, and the encoding bit rate BR is not limited to Formula 3, butanother formula may be used that draws an S-curve having the inflectionpoint IP as an inflection point (not limited to a sigmoid function).

Since the maximum value MAX and the inflection point IP are eachobtained from the resolution RS and the frame rate FR, Formula 3 is anexample of a formula that calculates the estimated video quality valueVQ from the resolution RS, the frame rate FR, and the encoding bit rateBR.

FIG. 4 schematically illustrates a graph representing the video qualityvalue obtained by Formula 3 for each encoding bit rate BR, given certainresolution RS and frame rate FR. In FIG. 4, the value of the inflectionpoint IP for the given resolution RS and frame rate FR is illustrated as“IP”. Also, in the case of FIG. 4, the maximum value MAX for the givenresolution RS and frame rate FR is 5.

In the embodiment, a formula that calculates the estimated video qualityvalue VQ from the resolution RS, the frame rate FR, and the encoding bitrate BR is not limited to that having the inflection point asillustrated in Formula 3 and FIG. 4, but the following Formula 4 may beused, for example.VQ=MAX−MAX·exp(−BR/a)  Formula 4

where “a” is a fixed coefficient whose suitable value is determined by,for example, an experiment or the like. MAX is the maximum value MAXthat has been already described, which is calculated by Formula 1 in theembodiment. BR is the encoding bit rate.

FIG. 5 schematically illustrates a graph representing the video qualityvalue obtained by Formula 4 for each encoding bit rate BR, given certainresolution RS and frame rate FR. As illustrated in FIG. 5, the graphdoes not have an inflection point, and the video quality value decreasesfrom the maximum value MAX (5 in the case of FIG. 5) while the encodingbit rate decreases.

In this case, the video quality calculator 16 may include processinglogic corresponding to Formula 4 to calculate the estimated videoquality value VQ, or may read data of the function represented byFormula 4 from a storage unit included in the video quality estimationapparatus 10 to execute the calculation of Formula 4. Alternatively,according to the relationship represented by Formula 4, a table may bestored in the storage unit in which values of the maximum value MAX, theencoding bit rate BR, and the estimated video quality value VQ areassociated with each other, from which an estimated video quality valueVQ is read out that corresponds to the input values (the maximum valueMAX and the encoding bit rate BR), to execute the calculation.

Note that although it has been described with FIG. 1 and FIG. 2 thathaving the inflection point is one of the properties of the videoquality, this is just an example of the properties of the video quality.Depending on the video, as illustrated in FIG. 5, the video qualityvalue may increase while the encoding bit rate increases, and mayconverge on the maximum value MAX without having an inflection point.For such a video, a formula that does not have an inflection point suchas Formula 4 can be used to precisely estimate the video quality. Also,if using Formula 4, the video quality estimation apparatus 10 may notinclude the inflection point calculator 14.

Although the method for obtaining or determining the resolution, theframe rate, and the encoding bit rate used as input values to the videoquality estimation apparatus 10 in the embodiment is not limited to aspecific method, the following method may be considered as an example.

For example, if a provider of the video distribution service estimatesthe video quality by using the video quality estimation apparatus 10,the provider can use the resolution, the frame rate, and the encodingbit rate that are used for the video distribution service as the inputvalues.

Also, for example, if a user of a network business company or the videodistribution service, who does not know the resolution, the frame rate,and the encoding bit rate that are used in the video distributionservice, estimates the video quality of the video distribution serviceby using the video quality estimation apparatus 10, the user may obtainmeta-information (e.g., MPD (Media Presentation Description) inMPEG-DASH) distributed from the server so as to obtain the resolution,the frame rate, and the encoding bit rate described in themeta-information, and to use them as the input values to the videoquality estimation apparatus 10.

Note that the encoding bit rate described in the meta-information is atarget bit rate (a set value to be achieved during the encoding). In acase where the actual encoding bit rate fluctuates considerably withrespect to the target bit rate, it is desirable to measure the actualencoding bit rate to be used as the input value. This is because themeasured encoding bit rate corresponds better with the video qualitythan the target bit rate. Therefore, as for the encoding bit rate, it isdesirable to use, as the input value, a bit rate that has been obtainedby measuring the payload of IP packets of the video transmitted by thevideo distribution service.

Here, if video and sound media are encrypted, and hence, each of themedia cannot be identified but only the total bit rate can be measured,the sound bit rate may be obtained from the meta-information, which isthen subtracted from the total bit rate measured with the IP packets, totreat the subtracted value as the encoding bit rate of the video. Notethat since the sound bit rate hardly fluctuates with respect to thetarget bit rate, the value obtained from the meta-information asdescribed above can be used.

Also, if the bit stream of the IP packets (the very data encoded byH.264 or H.265) can be accessed, measuring the bit rate of the datamakes it possible to use the measured bit rate as the input value to thevideo quality estimation apparatus 10.

The functionality of obtaining the resolution, the frame rate, and theencoding bit rate may be provided with the video quality estimationapparatus 10 as described above, or another device may provide thefunctionality, and inputs the value obtained on the device into thevideo quality estimation apparatus 10.

(Operational Steps)

Next, operations of the video quality estimation apparatus 10 configuredas described above, to which the method for estimating video qualityaccording to the embodiment is applied, will be described using aflowchart in FIG. 6. In the following, a case will be described as anexample in which a formula having the inflection point IP (e.g., Formula3) is used for estimating the video quality. Note that if using aformula not having an inflection point IP as Formula 4, it is notnecessary to calculate the inflection point IP at Step S2 below.

First, the maximum value calculator 12 calculates the maximum value MAXof the video quality value that is determined for each resolution RS andfor each frame rate FR where the resolution RS is the number of pixelsin one frame of the video, and the frame rate FR is the number of framesper unit time in the video (Step S1). The maximum value MAX of the videoquality value is, as described above, represented by a two-variableincreasing function that increases while the resolution RS and the framerate FR increase. At Step S1, the maximum value calculator 12 calculatesthe maximum value MAX by inputting certain resolution RS and frame rateFR into the two-variable increasing function.

In addition, by using the resolution RS and the frame rate FR, theinflection point calculator 14 calculates the inflection point IP, whichis a point where the curving direction changes on a curve drawn by thesigmoid function used in the video quality calculator 16 (Step S2). Thesigmoid function has the property of an S-curve that converges on acertain value when the input value increases or decreases. Theinflection point IP is, as described above, represented by atwo-variable increasing function that increases while the resolution RSand the frame rate FR increase. In other words, at Step S2, theinflection point calculator 14 calculates the inflection point IP byinputting the resolution RS and the frame rate FR, which are used as theinput at Step S1, into the two-variable increasing function.

Next, the video quality calculator 16 takes the encoding bit rate BR asthe input value, and calculates the estimated video quality value VQrepresented by the sigmoid function to which the maximum value MAX ofthe video quality value calculated at Step S1, and the inflection pointIP calculated at Step S2 are applied (Step S3). In other words, thevideo quality calculator 16 inputs a certain encoding bit rate BR, themaximum value MAX calculated at Step S1, and the inflection point IPcalculated at Step S2 into the sigmoid function (e.g., Formula 3) whosevariables are the encoding bit rate BR, the maximum value MAX, and theinflection point IP, to calculate the estimated video quality value VQ.

The coefficient c₇ is determined so that the higher convergence value ofthe encoding bit rate BR becomes the maximum value MAX of the videoquality value, and the lower convergence value of the encoding bit rateBR becomes the minimum value MIN of the video quality value. Also, theinflection point IP corresponds to the X-axis coordinate of theinflection point of the sigmoid function.

Note that c₁, c₂, c₃, c₄, c₅, c₆, and c₇ may be determined by the methodof least squares or the like so as to be optimized in a sense that thedifference becomes minimum between the video quality value and theestimated video quality value VQ obtained by the subjective evaluationexperiments.

Note that Step S1 and Step S2 may be executed by either of serialprocessing or parallel processing. Also, in the case of serialprocessing, whichever of Step S1 and Step S2 can be executed first.

(Summary of Embodiment)

As has been described so far, in a service of encoded video to be viewedand listened to, the video quality estimation apparatus 10 of theembodiment estimates the video quality value which is a valuequantifying the video quality felt by the user viewing and listening tothe encoded video.

On this account, the video quality estimation apparatus 10 calculatesthe video quality value that is determined by the resolution being thenumber of pixels in one frame of the video and the frame rate being thenumber of frames per unit time of the video. Also, the video qualityestimation apparatus 10 calculates an inflection point being a point atwhich the curving direction changes on a curve drawn by a sigmoidfunction having a property of an S-curve that converges on a certainvalue when the input value increases or decreases, based on theresolution and the frame rate. Then, the video quality estimationapparatus 10 takes an encoding bit rate being the average amount of dataper unit time of the video as the input value, and calculates theestimated video quality value represented by the sigmoid function towhich the calculated maximum value and the calculated inflection pointare applied.

Note that the coefficient of the sigmoid function is determined so thatthe higher convergence value of the sigmoid function becomes the maximumvalue of the video quality value, and the lower convergence value of thesigmoid function becomes the minimum value of the video quality value.Also, the maximum value of the video quality value is represented by atwo-variable increasing function that increases while the resolution andthe frame rate increase, and the inflection point is represented by atwo-variable increasing function that increases while the resolution andthe frame rate increase.

Also, the maximum value calculator may be configured to include amaximum value calculator configured to calculate a maximum value of thevideo quality value from a resolution of the video and a frame rate ofthe video; and a video quality calculator configured to calculate anestimated video quality value corresponding to an encoding bit ratehaving been input, based on a predetermined relationship between theencoding bit rate of the video and the video quality value, wherein thepredetermined relationship is a relationship in which the video qualityvalue increases while the encoding bit rate increases, and the videoquality value converges on the maximum value calculated by the maximumvalue calculator.

As described above, in the video quality estimation apparatus 10 towhich the method for estimating video quality according to theembodiment is applied, a model for estimating the video quality value isbuilt by using a sigmoid function.

Since a sigmoid function can be represented by an S-curve that convergeson a certain value while the input value increases or decreases,Property 1 described above can be taken into account. Also, since theconvergence value of a sigmoid function can be determined by thecoefficient, by determining the coefficient so that the higherconvergence value of the sigmoid function becomes the maximum value ofthe video quality value, and the lower convergence value of the sigmoidfunction becomes the minimum value of the video quality value, Property2 and Property 3 described above can be also taken into account.

Furthermore, since the X-axis coordinate of the inflection point on theS-curve of a sigmoid function can be determined by the coefficient, bymodelling the coefficient so that the X-axis coordinate of theinflection point IP determined by the coefficient increases while theresolution RS and the frame rate FR increase, Property 4 described abovecan be also taken into account.

Therefore, by building a model for estimating the video quality value byusing a sigmoid function as in the video quality estimation apparatus 10to which the method for estimating video quality according to embodimentis applied, it is possible to calculate the estimated video qualityvalue VQ by considering the resolution RS and the frame rate FR inaddition to the encoding bit rate BR.

Furthermore, estimating the estimated video quality value VQ by usingsuch an apparatus, a method, and a program makes it possible not only tograsp quantitatively the quality of the video distribution service of aservicing company and other competing companies, but also to utilizethese results for marketing and service improvement.

Also, by utilizing the result of the estimated video quality value VQ,and designing and controlling the distribution parameters to maximizethe video quality value, it is possible to raise the video quality. Asfurther consequences, improvement in the customer satisfaction andcontribution to raising the revenue of the video distribution servicecan be also expected.

As has been described above so far, the model taking Properties 1 to 4into account is built by using the sigmoid function in the embodiment.Since the sigmoid function can be represented by an S-curve thatconverges on a certain value while the input value increases ordecreases, Property 1 can be modeled. Also, since the convergence valueof the sigmoid function can be determined by the coefficient, bydetermining the coefficient so that the higher convergence value of thesigmoid function becomes the maximum value of the video quality value,and the lower convergence value of the sigmoid function becomes theminimum value of the video quality value, Property 2 and Property 3 canbe taken into account.

Furthermore, since the X-axis coordinate of the inflection point on theS-curve of the sigmoid function can be determined by the coefficient, bymodelling the coefficient so that the X-axis coordinate of theinflection point IP determined by the coefficient increases while theresolution RS and the frame rate FR increase, Property 4 can be alsotaken into account.

Therefore, by using the model using the sigmoid function, the apparatus,the method, and the program capable of precisely estimating the videoquality value can be realized while considering the resolution and theframe rate in addition to the encoding bit rate.

Note that a function representing an S-curve whose output valueconverges on a certain value when the input value increases or decreasesis not limited to the sigmoid function. A function other than thesigmoid function may be used as a function representing such an S-curve.Also, a function not having an inflection point as Formula 4 may beused. By using such a function not having an inflection point, theapparatus, the method, and the program capable of precisely estimatingthe video quality value can be realized while considering the resolutionand the frame rate in addition to the encoding bit rate.

This invention is not limited to the embodiments, but can be modified tobe used in various ways within the scope of this invention.

In other words, this invention is not limited to the embodiments as theyare, but in actual applications, can be realized with modifying theelements within the scope of this invention. Also, by combining multipleelements disclosed in the embodiments, various inventions can be formed.For example, some elements may be deleted among all of the elements inan embodiment. Furthermore, elements in different embodiments may becombined appropriately.

The present patent application claims priority based on Japanese PatentApplication No. 2014-232691, filed on Nov. 17, 2014, and the entirecontents of Japanese Patent Application No. 2014-232691 are incorporatedherein by reference.

LIST OF REFERENCE SYMBOLS

-   10 video quality estimation apparatus-   12 maximum value calculator-   14 inflection point calculator-   16 video quality calculator

The invention claimed is:
 1. A video quality estimation apparatus usedfor an encoded video to be viewed and listened to, to estimate a videoquality value being a value quantifying a video quality being quality ofthe video felt by a user when viewing and listening to the video, thevideo quality estimation apparatus comprising: a maximum valuecalculator configured to calculate a maximum value of the video qualityvalue from a resolution of the video and a frame rate of the video; anda video quality calculator configured to calculate an estimated videoquality value corresponding to an encoding bit rate having been input,based on a predetermined relationship between the encoding bit rate ofthe video and the video quality value, wherein the predeterminedrelationship is a relationship in which the video quality valueincreases while the encoding bit rate increases, and the video qualityvalue converges on the maximum value calculated by the maximum valuecalculator.
 2. A non-transitory computer readable medium including avideo quality estimation program executed by a computer used as thevideo quality estimation apparatus according to claim 1 to executeprocesses of the calculators included in the video quality estimationapparatus.
 3. A video quality estimation apparatus used for an encodedvideo to be viewed and listened to, to estimate a video quality valuebeing a value quantifying a video quality being quality of the videofelt by a user when viewing and listening to the video, the videoquality estimation apparatus comprising: a maximum value calculatorconfigured to calculate a maximum value of the video quality value,based on a resolution being a number of pixels in one frame of the videoand a frame rate being a number of frames per unit time of the video, aninflection point calculator configured to calculate an inflection pointbeing a point at which a curving direction changes on a curve drawn by asigmoid function having a property of an S-curve that converges on acertain value when an input value increases or decreases, based on theresolution and the frame rate, and a video quality calculator configuredto calculate an estimated video quality value by inputting an encodingbit rate being an average amount of data per unit time of the video, themaximum value of the video quality value calculated by the maximum valuecalculator, and the inflection point calculated by the inflection pointcalculator, into the sigmoid function.
 4. The video quality estimationapparatus according to claim 3, wherein a coefficient of the sigmoidfunction is determined so that a higher convergence value of the sigmoidfunction becomes the maximum value of the video quality value, and alower convergence value of the sigmoid function becomes a minimum valueof the video quality value.
 5. The video quality estimation apparatusaccording to claim 3, wherein the maximum value of the video qualityvalue is represented by a two-variable increasing function thatincreases while the resolution and the frame rate increase, and theinflection point is represented by a two-variable increasing functionthat increases while the resolution and the frame rate increase.
 6. Amethod for estimating video quality executed by a video qualityestimation apparatus used for an encoded video to be viewed and listenedto, to estimate a video quality value being a value quantifying a videoquality being quality of the video felt by a user when viewing andlistening to the video, the method comprising: a maximum valuecalculating step for calculating a maximum value of the video qualityvalue from a resolution of the video and a frame rate of the video, anda video quality calculating step for calculating an estimated videoquality value corresponding to an encoding bit rate having been input,based on a predetermined relationship between the encoding bit rate ofthe video and the video quality value, wherein the predeterminedrelationship is a relationship in which the video quality valueincreases while the encoding bit rate increases, and the video qualityvalue converges on the maximum value calculated by the maximum valuecalculating step.
 7. A method for estimating video quality executed by avideo quality estimation apparatus used for an encoded video to beviewed and listened to, to estimate a video quality value being a valuequantifying a video quality being quality of the video felt by a userwhen viewing and listening to the video, the method comprising:calculating a maximum value of the video quality value, based on aresolution being a number of pixels in one frame of the video and aframe rate being a number of frames per unit time of the video,calculating an inflection point being a point at which a curvingdirection changes on a curve drawn by a sigmoid function having aproperty of an S-curve that converges on a certain value when an inputvalue increases or decreases, based on the resolution and the framerate, and calculating an estimated video quality value by inputting anencoding bit rate being an average amount of data per unit time of thevideo, the maximum value, and the inflection point, into the sigmoidfunction.
 8. The method for estimating the video quality according toclaim 7, wherein a coefficient of the sigmoid function is determined sothat a higher convergence value of the sigmoid function becomes themaximum value of the video quality value, and a lower convergence valueof the sigmoid function becomes a minimum value of the video qualityvalue.
 9. The method for estimating the video quality according to claim7, wherein the maximum value of the video quality value is representedby a two-variable increasing function that increases while theresolution and the frame rate increase, and the inflection point isrepresented by a two-variable increasing function that increases whilethe resolution and the frame rate increase.